JP2002246047A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve responsiveness with respect to a change in load of a fuel cell system, using a liquid fuel superior in mountability on a moving body. SOLUTION: The fuel cell system comprises a reformer 7 for producing a fuel gas containing hydrogen from a hydrocarbon liquid fuel, such as a gasoline and a fuel cell 9 into which the fuel gas is supplied for generating power, where an exhaust gas circulation passage 10 for circulating part of an anode exhaust gas or a cathode exhaust gas from the fuel cell to the reformer side and a circulation blower 6 are provided, and a fuel carburetor 4 is provided for phase vaporizing the liquid fuel injected and supplied from the injector 3 in a high-temperature atmosphere with the circulated exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system for generating power using a fuel gas containing hydrogen generated from a liquid fuel.

[0002]

2. Description of the Related Art A fuel cell is a cell that generates power by an electrochemical reaction using hydrogen or a hydrocarbon gas as fuel and air containing oxygen or acid as an oxidant. When a hydrocarbon-based gas is used as a fuel, generally, a part or all of the hydrocarbon-based fuel is reformed into hydrogen using a reaction represented by the following formulas (1) and (2) to produce a fuel. Supply to the fuel electrode of the battery.

C _n H _{2n + 2} + nH ₂ O → nCO + (n + 2) H ₂ (1) CO + H ₂ O → CO ₂ + H ₂ (2) As shown in the reaction formula (1), In addition, water is required for reforming hydrocarbon-based gas, while fuel cells use H ₂
The exhaust gas contains sufficient moisture to generate O. Therefore, in order to effectively use the fuel gas or the oxidizing gas in the entire system, a fuel cell system that recirculates the exhaust gas has been studied.

For example, in the system disclosed in JP-A-11-233129, in a solid oxide fuel cell power generation system, a part of the anode exhaust gas of a fuel cell is mixed with a supply fuel gas and provided in a recirculation system. Once cooled by heat exchange with the low-temperature reflux gas after passing through the condenser in the regenerative heat exchanger, it is also cooled in the condenser to condense and separate excess water vapor in the exhaust gas, and then to the fuel cell anode inlet. The supply prevents a decrease in the electromotive force of the fuel cell and improves the system efficiency. A circulation blower for circulating the fuel gas is installed after passing through the condenser, so that the circulation blower can be operated at normal temperature.

However, this fuel cell system has the following problems. That is, when the fuel cell system is applied to a moving object, it is important that the volume of the fuel cell system is as small as possible. Therefore, it is desirable that the fuel source is liquid rather than gas. In this respect, since the above system uses a gas having a lower energy density as a fuel source than a liquid, the volume of the fuel cell system including the fuel storage becomes larger than that of the liquid system, and as it is mounted on a moving body as it is. Not suitable for

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 2000-100462, for example, liquid fuel is sent to an evaporator according to the load of a fuel cell, and the liquid fuel is vaporized and supplied to a reformer. It is possible to solve the problem of mountability by using the techniques described above together. However, in the system in which the fuel gas is supplied to the fuel cell or the reformer while evaporating the fuel in the evaporator in the liquid phase, sufficient responsiveness is not necessarily obtained in a system having a large load fluctuation of the fuel cell such as a moving body. Can not be obtained. Further, even when the system is stopped, the vaporization of the liquid fuel in the evaporator cannot be stopped, and it is necessary to consider the treatment of the vaporized fuel after the system is stopped. Further, coking due to fuel vaporization in the evaporator is liable to occur, which causes a problem that the performance of the evaporator deteriorates and the efficiency of the system decreases. An object of the present invention is to provide a fuel cell system that solves such a conventional problem.

[0007]

According to a first aspect of the present invention, there is provided a fuel gas generator for generating a fuel gas containing hydrogen from a liquid fuel;
A fuel cell system comprising: a fuel cell configured to generate power by receiving the fuel gas; an exhaust gas circulating device configured to recirculate a part of exhaust gas of the fuel cell to the fuel gas generating unit; And a fuel vaporizer for supplying and evaporating a liquid fuel.

According to a second aspect of the present invention, there is provided the exhaust gas circulating apparatus according to the first aspect of the present invention, wherein an exhaust gas circulating flow path for introducing exhaust gas from a fuel cell into a fuel gas generating section, and a circulating blower for pressure-feeding the exhaust gas from the exhaust gas circulating flow path. And a fuel injection unit that injects and supplies fuel to the fuel carburetor, and the fuel carburetor is provided upstream of the circulation blower.

According to a third aspect of the present invention, in each of the above-mentioned aspects, a water supply device for supplying water to a high temperature atmosphere by the recirculated exhaust gas to vaporize the water is provided.

According to a fourth aspect of the present invention, the water supply device according to the third aspect of the invention has a water injection unit configured to inject and supply water into the recirculated exhaust gas.

According to a fifth aspect, in the fourth aspect,
A water injection supply unit was provided at the same location as the fuel injection unit.

In a sixth aspect, the water injection supply section of the fifth aspect is provided upstream of the fuel injection section.

According to a seventh aspect of the present invention, the water supply device according to the third to sixth aspects includes a steam flow rate detecting device for detecting the amount of steam in the recirculated exhaust gas, and controls the amount of supplied water in accordance with the detected amount of steam. It was configured to be.

According to an eighth aspect, the fuel vaporizer according to the first to seventh aspects includes means for detecting the amount of unreacted liquid fuel remaining in the recirculated exhaust gas. The fuel supply amount is controlled accordingly.

According to a ninth aspect, in the first to eighth aspects, a solid oxide fuel cell is provided as the fuel cell.

In a tenth aspect based on the ninth aspect, an anode exhaust gas of a fuel cell is used as the exhaust gas.

According to an eleventh aspect, in the ninth aspect, the twelfth aspect uses the cathode exhaust gas of the fuel cell as the exhaust gas. Prepare.

[0018]

[Operation and Effect] In each of the inventions following the first invention,
The anode exhaust gas or the cathode exhaust gas discharged from the fuel cell is returned to the fuel gas generation section of the fuel cell system, for example, the anode section of the fuel cell or the reformer through the exhaust gas circulation device. On the other hand, the fuel vaporizer injects and supplies liquid fuel into a high-temperature atmosphere due to the recirculated exhaust gas. Thereby, the fuel is quickly vaporized and supplied to the fuel cell or the reformer. Since the liquid fuel is vaporized and supplied in this manner, good responsiveness to changes in the load of the fuel cell can be obtained.

On the other hand, since the liquid fuel is rapidly vaporized in the fuel vaporizer, the liquid fuel does not directly touch a high-temperature portion such as the inner wall of the vaporizer, thereby preventing coking by the liquid fuel. Therefore, performance degradation of a portion to be vaporized can be suppressed. Further, the system configuration is simplified, and the cost can be reduced.

According to the second invention, when a circulation blower is provided as a means for forced circulation in the exhaust gas circulation device, fuel vaporization is performed by the fuel vaporizer on the upstream side, so that the fuel gas and the fuel gas in the circulation blower are increased. By reducing the temperature of the exhaust gas, its heat-resistant specification can be reduced, and the reliability and cost of the circulation blower can be improved accordingly.

According to the third or fourth aspect of the present invention, since water is supplied to the exhaust gas to generate steam, it is possible to control the amount of steam in the circulating gas. Thus, when the reformer is used, it is possible to efficiently perform a reforming reaction of a fuel gas equivalent to steam or more contained in the recirculated exhaust gas in the reformer. Further, since the temperature of the recirculated exhaust gas is reduced by the vaporization of water, the durability and reliability of the circulating blower can be further improved when a circulating blower is used. Since water does not cause a problem of coking, it does not need to be vapor-phase vaporized, and may be provided with a mechanism capable of atomizing water to such an extent that liquid fuel is not accumulated. For example, a structure in which a material such as an iron ball, which withstands the temperature of the anode or cathode exhaust gas and has resistance to reduction, is incorporated in the vaporizer can be applied. On the other hand, when water is sprayed into the exhaust gas and gas phase is vaporized,
Responsiveness to a change in the load of the fuel cell can be improved.

Further, as in the fifth aspect of the invention, by integrating the water injection supply section with the fuel injection section of the fuel carburetor, the structure can be simplified and made compact, and the cost can be reduced. . In this configuration, water has a greater latent heat than hydrocarbon-based liquid fuels such as gasoline,
Water can be vaporized more stably if vaporized before liquid fuel. Therefore, it is desirable that the water injection supply unit is provided upstream of the fuel injection unit as in the sixth invention.

Further, in the seventh or eighth invention, the supply amount of water or liquid fuel is controlled based on the amount of water vapor or the amount of fuel component in the exhaust gas. It can be adjusted to the optimal amount in terms of system efficiency. In addition, since unnecessary fuel supply can be avoided, the residual amount of vaporized fuel after the system stops is small,
The treatment is easy.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, parts common to each other will be denoted by the same reference numerals, and redundant description will be omitted in principle.

FIG. 1 is a schematic configuration of a fuel cell system according to a first embodiment of the present invention. The fuel cell system according to this embodiment is an oxygen ion conduction type solid oxide fuel cell (SO 2) that generates power using hydrogen or hydrocarbons as fuel.
In FC), for example, a hydrocarbon-based liquid fuel such as gasoline is used as a fuel source, and a part of the fuel exhaust gas after power generation by the fuel cell main body 9 is passed through the fuel vaporizer 4 to the fuel cell anode inlet 9a. It is designed to be refluxed.

The supplied fuel is stored in a liquid state in a fuel tank 1, supplied from a fuel supply passage 2 to an injector 3, and injected into a fuel carburetor 4. Further, among the anode exhaust gas from the anode outlet 9b of the fuel cell, the anode exhaust gas that is recirculated through the anode exhaust gas circulation passage 10 is supplied to the fuel vaporizer 4, and the fuel vaporizer 4 injects the anode exhaust gas from the injector 3 in the fuel vaporizer 4. The supplied fuel and the circulating anode exhaust gas are mixed. The fuel spray is vaporized to be a mixed fuel gas, and is supplied to the reformer 7 via the fuel gas supply passage 5 and the circulation blower 6.

The solid oxide fuel cell used in this fuel cell system generally has an anode exhaust gas temperature of 800 to 1000 ° C.
And the high temperature, the gaseous phase vaporization of the liquid fuel is easy. Since the temperature of the mixed fuel gas is lower than that of the circulating anode exhaust gas due to vapor phase vaporization, high-temperature fuel and water vapor do not pass through the circulating blower 6, and improvement in the reliability of the circulating blower 6 can be expected.

In the case of steam reforming, since the endothermic reaction is performed, the temperature of the reformer 7 tends to decrease. However, by utilizing the heat of the combustor 13 for mixing and burning the cathode exhaust gas and the anode exhaust gas, The reforming reaction can be performed efficiently. The reformed fuel gas is supplied to the fuel gas supply passage.
The fuel gas is supplied to the fuel cell anode inlet 9a through the fuel cell 8 and used for power generation. Unused gas and water vapor generated by the power generation are discharged from the fuel cell anode outlet 9b as anode exhaust gas.

The supply air is supplied from an air flow path 16 via an air source 17 composed of a blower or a compressor, etc., and is heated by heat exchange with a combustion exhaust gas 15 from a combustor 13 in an air preheating exchanger 14. Fuel cell body
The fuel gas is supplied to the fuel cell cathode inlet 9c and used for power generation, and unused air is discharged from the fuel cell cathode outlet 9d. Cathode exhaust gas discharged from the fuel cell cathode outlet 9d passes through the cathode exhaust gas passage 12 to the combustor 1.
3 and, at the same time, is combusted with the non-refluxed portion of the anode exhaust gas from the anode outlet 9b of the fuel cell and discharged as exhaust gas.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, similarly to the first embodiment, the supply fuel stored in the fuel tank 1 in a liquid state is converted into the recirculated anode exhaust gas out of the anode exhaust gas from the fuel cell anode outlet 9b. The fuel spray from the injector 3 is mixed and supplied to the fuel cell. However, in this embodiment, the fuel cell main body 9 is an internal reforming type,
The mixed fuel gas of the recirculated exhaust gas and the supplied fuel mixed in the fuel vaporizer 4 is supplied directly to the fuel cell fuel gas inlet 8a via the circulation blower 6. In the case of an internal reforming type fuel cell, the heat of the fuel cell is deprived by the reforming reaction,
The amount of heat can be supplemented by the combustor 13 generated by the combustion of the air exhaust gas and the fuel exhaust gas.

FIG. 3 shows a third embodiment of the present invention. In this embodiment, in the same fuel cell system as in the first embodiment, a configuration for injecting water into the fuel vaporizer 4 is added, and the circulation supplied to the fuel vaporizer 4 via the anode exhaust gas circulation flow path 10 is further added. The amount of water vapor in the anode exhaust gas (mo1 / se
c), and the remaining amount of the unused fuel component is detected by a detecting device such as a differential pressure type steam flow meter 18 or a fuel component meter 19 including an optical humidity sensor.

More specifically, the water stored in the water tank 20 is supplied to the injector 22 through the water supply flow path 21,
It is injected into the fuel carburetor 4. Among the anode exhaust gas from the anode outlet 9b of the fuel cell, the anode exhaust gas which is recirculated through the anode exhaust gas circulation passage 10 is supplied to the fuel vaporizer 4. The water spray (water vapor) injected from 22 and the circulating anode exhaust gas are mixed. The injected water deprives the heat of the circulating anode exhaust gas of some degree when it evaporates, but does not prevent the fuel spray from evaporating.

The mixed fuel gas mixed in the fuel vaporizer 4 is supplied to the reformer 7 through the fuel gas supply passage 5 and the circulation blower 6. Since the temperature of the mixed fuel gas is lower than that of the circulating exhaust gas due to vaporization, high-temperature fuel and water vapor do not pass through the circulating blower 6. The reformed fuel gas is supplied to the fuel cell anode inlet 9a through the fuel gas supply flow path 8 and used for power generation. Unused fuel gas and water vapor generated by the power generation are converted into anode exhaust gas from the fuel cell anode outlet 9b as anode exhaust gas. Is discharged.

By the way, the amount of fuel used in the fuel cell is
The usage amount corresponding to the output load of the fuel cell can be uniquely calculated from the chemical reaction formula of the power generation. However, in actual operation of the fuel cell, it is necessary to supply more fuel than the fuel amount obtained from the chemical reaction formula. As a result,
Generally, the anode exhaust gas discharged from the fuel cell anode outlet 9b contains unused fuel components. Therefore, in this embodiment, the amount of unused fuel contained in the circulating anode exhaust gas is measured by the fuel component meter 19, and the shortage with respect to the required fuel supply amount obtained from the load of the fuel cell is determined by the injector 3.
Is controlled by spraying. Thereby, the fuel use efficiency can be improved without circulating useless fuel. In addition, problems such as caulking in the piping due to unnecessary fuel circulation are eliminated. Further, in order to reform a hydrocarbon-based liquid fuel such as gasoline, steam equivalent to the fuel to be reformed is required as described above. Therefore, the amount of steam contained in the circulating anode exhaust gas is measured by the steam flow meter 18, and the shortage of steam required for efficient reforming in the reformer 7 is sprayed by the injector 22. . By this control, efficient steam reforming of the fuel can be performed.

As described above, the efficiency of the fuel cell system can be improved by controlling the amounts of fuel and water supplied by the load of the fuel cell. FIG. 4 is a flowchart showing a schematic procedure of the fuel / water supply amount control. This shows processing steps periodically executed by a controller (not shown) including a microcomputer and its peripheral devices. Hereinafter, description will be made in order. It should be noted that the symbol “S” in the following description and in the drawings represents a processing step. S1: A required load on the fuel cell is obtained from the accelerator operation amount and the moving speed by the driver. S2, S5: From the signals of the fuel component meter 19 and the steam flow meter 18, the amount of residual fuel and the amount of steam in the anode exhaust gas are detected, respectively. S3, S6: Based on the required load and the detected residual fuel amount, a preset map as shown in FIG. 5 is searched to find the fuel supply amount. As shown, a predetermined map is searched to determine the water supply amount. S4, S7: Inject and supply the fuel amount and the water supply amount searched from the injector 3 and the injector 22, respectively.

In this embodiment, the configuration of the water injection is added to the first embodiment. However, the configuration of the water injection is not limited to this, and can be applied to the second embodiment.

FIG. 7 shows a fourth embodiment of the present invention. In this embodiment, a high-temperature exhaust gas discharged from a cathode side is recirculated in a proton-conductive solid oxide fuel cell that generates power using hydrogen or hydrocarbons as fuel. That is, a hydrocarbon-based liquid fuel such as gasoline is used as a fuel source, and a part of the cathode exhaust gas generated by the fuel cell main body 9 is returned to the fuel cell anode inlet 9a via the fuel vaporizer 4. . Further, a water supply device similar to that of the third embodiment is provided.

In detail, of the cathode exhaust gas from the cathode outlet 9d of the fuel cell, the cathode exhaust gas which is recirculated through the cathode exhaust gas circulation channel 23 is supplied to the fuel carburetor 4. 3, fuel (water vapor) injected from the injector 22, and the recirculated cathode exhaust gas are mixed. At this time, the cathode exhaust gas of the proton-conductive solid oxide fuel cell is at a high temperature, the gaseous vaporization of the liquid fuel and water is easy, and the injected water deprives the calorie of the circulating cathode exhaust gas during vaporization. However, it is not enough to prevent vaporization of the atomized supply fuel. The mixed fuel gas mixed in the fuel vaporizer 4 is supplied to the reformer 7 through the fuel gas supply channel 5 and the circulation blower 6. Since the temperature of the mixed fuel gas is lower than that of the circulating cathode exhaust gas due to gas phase vaporization, high-temperature fuel and water vapor do not pass through the circulating blower 6. The reformed fuel gas is supplied to the fuel gas supply passage 8
Is supplied to the fuel cell fuel electrode 9a and used for power generation, and is discharged from the fuel cell fuel electrode outlet 9b as anode exhaust gas.

The supply air from the air source 17 is supplied to the air passage 16
From the combustor 1 in the air preheating exchanger 14.
The fuel gas is heated by heat exchange with the combustion exhaust gas 15 from the fuel cell 3, and is supplied to the fuel cell cathode inlet 9c of the fuel cell body 9 and used for power generation.
It is discharged from d. A part of the cathode exhaust gas discharged from the fuel cell cathode outlet 9d is supplied to the fuel carburetor 4 via the cathode exhaust gas circulation channel 23, while the remainder is supplied to the combustor 13 via the cathode exhaust gas channel 12; At the same time, it is burned together with the anode exhaust gas supplied to the combustor 13 through the anode exhaust gas passage 11 and discharged as exhaust gas.

FIG. 8 is a flowchart showing a schematic procedure of controlling the fuel / water supply amount in this embodiment. In the control of this embodiment, the fuel supply amount is controlled in an open loop based on the operation load, while the water supply amount is fed back to an optimum amount based on a signal from the steam flow meter 18. The flow chart shows processing steps periodically executed by a controller (not shown) including a microcomputer and its peripheral devices as in FIG. Hereinafter, description will be made in order. S1: The required load on the fuel cell is determined from the accelerator operation amount and the moving speed by the driver. S2: The amount of water vapor in the cathode exhaust gas is detected from the signal of the water vapor flow meter 18. S3, S5: Based on the required load, the fuel supply amount is obtained by referring to a map set in advance as shown in FIG. 9, and the detected steam amount is referred to a map set in advance as shown in FIG. To determine the water supply. S4, S6: The fuel amount and the water supply amount thus found are injected and supplied from the injectors 3 and 22, respectively.

This embodiment is a system in which the reformer is provided outside the fuel cell. The configuration in which the cathode exhaust gas is circulated to the fuel cell main body 9 via the fuel vaporizer 4 is the same as in the second embodiment. It can also be applied to a fuel cell system that performs reforming inside a fuel cell.For example, a high-temperature exhaust gas can be obtained in an internal reforming type fuel cell system with a high operating temperature. Fuel cells are advantageous in vaporizing fuel and water.

As the reformer 7, any of a steam reforming type (SR) and a partial oxidation reforming type (ATR) can be applied. Further, in the above-described embodiment, in order to compensate for the temperature drop of the reformer 7 or to heat the supplied air,
However, the heat source is not limited to this, and a method of heating the outside of the reformer 7 with a burner or the like,
A method of using a separately provided heat source to maintain the temperature of the fuel cell can also be applied.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a fuel cell system according to the present invention.

FIG. 2 is a schematic configuration diagram of a second embodiment of a fuel cell system according to the present invention.

FIG. 3 is a schematic configuration diagram of a third embodiment of the fuel cell system according to the present invention.

FIG. 4 is a flowchart showing a control routine according to the third embodiment.

FIG. 5 is an explanatory diagram of a fuel supply amount map used for control in the third embodiment.

FIG. 6 is an explanatory diagram of a water supply amount map used for control of the third embodiment.

FIG. 7 is a schematic configuration diagram of a fourth embodiment of the fuel cell system according to the present invention.

FIG. 8 is a flowchart showing a control routine according to the fourth embodiment.

FIG. 9 is an explanatory diagram of a fuel supply amount map used for control of the fourth embodiment.

FIG. 10 is an explanatory diagram of a water supply amount map used for control of the fourth embodiment.

[Explanation of symbols]

 Reference Signs List 1 fuel tank 2 fuel supply passage 3 fuel injector 4 fuel vaporizer 5 6 circulation blower 7 reformer 8 fuel gas supply passage 9 fuel cell body 9a anode inlet 9b anode outlet 9c cathode inlet 9d cathode outlet 10 exhaust gas circulation flow Road 12 Cathode exhaust gas flow path 13 Combustor 14 Heat exchanger for air preheating 15 Exhaust flow path 16 Air flow path 17 Air source 18 Steam flow meter 19 Remaining fuel component meter 20 Water tank 21 Water supply flow path 22 Water injector 23 Cathode exhaust gas circulation channel

Claims (12)

[Claims] 1. A fuel cell system comprising: a fuel gas generation unit configured to generate a fuel gas containing hydrogen from a liquid fuel; and a fuel cell configured to generate power by receiving the fuel gas. A fuel cell system comprising: an exhaust gas circulating device for returning a fuel gas to a fuel gas generating unit; and a fuel vaporizer for supplying and vaporizing a liquid fuel in a high-temperature atmosphere by the recirculated exhaust gas. 2. The fuel cell system according to claim 1, wherein, as the exhaust gas circulating device, an exhaust gas circulating channel for introducing exhaust gas from a fuel cell into a fuel gas generating unit, and an exhaust gas in the exhaust gas circulating channel are pumped. A fuel cell system comprising: a circulation blower; a fuel injection unit for injecting and supplying fuel to the fuel carburetor; and the fuel carburetor provided upstream of the circulation blower. 3. The fuel cell system according to claim 1, further comprising a water supply device that supplies water to a high-temperature atmosphere by the recirculated exhaust gas and vaporizes the water. 4. The fuel cell system according to claim 3, wherein the water supply device includes a water injection unit configured to inject water into the recirculated exhaust gas. 5. The fuel cell system according to claim 4, wherein the fuel vaporizer and the water supply device are provided at the same location. 6. The fuel cell system according to claim 5, wherein the water injection supply unit is provided upstream of the fuel injection unit. 7. The fuel cell system according to claim 3, further comprising a steam flow rate detecting device for detecting a steam amount in the recirculated exhaust gas, and controlling a supply water amount according to the detected steam amount. The configured fuel cell system. 8. The fuel cell system according to claim 1, further comprising: means for detecting the amount of unreacted liquid fuel remaining in the recirculated exhaust gas by the fuel vaporizer. A fuel cell system configured to control a supplied fuel amount according to the amount. 9. The fuel cell system according to claim 1, further comprising a solid oxide fuel cell as the fuel cell. 10. The fuel cell system according to claim 9, wherein an anode exhaust gas of a fuel cell is used as the exhaust gas. 11. The fuel cell system according to claim 9, wherein a cathode exhaust gas of a fuel cell is used as the exhaust gas. 12. The fuel cell system according to claim 1, further comprising a reformer as the fuel gas generator.